Table 2.
Final multivariable analysis for venous thromboembolism risk within six weeks of delivery in derivation cohort
| Variable | Model 1 (based on backwards elimination): odds ratio* (95% CI) | β coefficients |
|---|---|---|
| Smoker (latest record before delivery) | 1.25 (0.97 to 1.62) | 0.22684105 |
| Varicose veins | 3.39 (2.25 to 5.10) | 1.2210805 |
| Comorbidities (heart, kidney, or inflammatory bowel disease) | 2.33 (1.47 to 3.71) | 0.8476927 |
| Pre-eclampsia/eclampsia | 2.06 (1.32 to 3.20) | 0.72127433 |
| Diabetes | 1.52 (0.97 to 2.39) | 0.42119233 |
| Nulliparous (antenatal) | Reference | – |
| Parity 1 | 1.18 (0.91 to 1.53) | 0.16456948 |
| Parity 2 | 1.62 (1.13 to 2.33) | 0.48143018 |
| Parity 3 or more | 1.76 (1.56 to 2.68) | 0.5664196 |
| Postpartum haemorrhage | 1.65 (1.21 to 2.24) | 0.50183134 |
| Spontaneous/assisted vaginal delivery | Reference | – |
| Elective caesarean section | 1.76 (1.26 to 2.44) | 0.56321456 |
| Emergency caesarean section | 2.11 (1.60 to 2.80) | 0.75035197 |
| Stillbirth | 3.16 (1.29 to 7.73) | 1.1514008 |
| Postpartum infection | 2.99 (2.07 to 4.33) | 1.0969922 |
| Fractional polynomial transformed | ||
| Age^3 | – | −0.00007986 |
| Age^3×ln (age) | – | 0.00002147 |
| BMI^3 | – | 0.00026641 |
| BMI^3×ln (BMI) | – | −0.00006501 |
| Infant birth weight^−2 | – | −22156315 |
| Infant birth weight^−2×ln (birth weight) | – | 3455223.4 |
| Constant† | – | −9.103121 |
Multiple imputation was carried out for missing body mass index (BMI) and birthweight data (10 imputations). Age was included in model as a priori predictor. Predictors were retained in model at 10% level of significance.
*For binary variables, odds ratio is based on women without particular risk factor under study.
†Average across population. Constant was re-estimated after adjustment of model for optimism to ensure that overall calibration was maintained.